Distribution of a New Myelomonocytic Antigen (L1) in Human Peripheral Blood Leukocytes: Immunofluorescence and Immunoperoxidase Staining Features in Comparison with Lysozyme and Lactoferrin

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Abstract
The LI antigen is a highly immunogenic protein of about 36,500 daltons that can be purified from granulocytes with good yield. Immunocytochemistry with a rabbit anti-serum raised against LI showed it to be present in the cytoplasm of vjrtually all resting peripheral neutrophils and monocytes. Moreover, immunofluorescence staining demonstrated variable expression of LI on the plasma membrane of both these cell types, usually along with lysozyme. This indicated that LI represents a secretory product like lysozyme as their coexpression on the surface of vital cells was contrasted by the absence of lactoferrin. Cytoplasmic LI was well preserved by both precipitating and cross-linking fixatives, the latter being preferable to avoid leaching out of antigenic material and to obtain good cellular morphology. Thus, fixation for 3 minutes at room temperature in glutaraldehyde (l%)–formaldehyde (3%) afforded excellent immunoperoxidase staining, particularly when a calcium-containing buffer was used. LI was not found in eosinophilic granulocytes or in resting B- and T-lymphocytes. Neither did blast transformation of lymphocytes seem to induce LI expression.